CVD showerhead reactors employ a perforated or porous planar surface to dispense reactant and carrier gases as uniformly as possible over a second parallel planar surface. This configuration can be used for continuous batch processing of multiple substrates or processing of single round wafers. Wafers are generally heated to a process temperature at which the reactant gases react and deposit a film on the wafer surface.
Showerhead reactors, or parallel-plate reactors, lend themselves to implementation of plasma-enhanced processes, e.g., plasma-enhanced chemical vapor deposition (PECVD). In most PECVD reactors the top and bottom electrodes are about the same size. The wafer electrode may be a substrate support and be grounded and the showerhead may have RF power applied. Bias RF power may be applied to the substrate support. The applied RF in the showerhead may necessitate insulating sections in the gas supply system to avoid creating a parasitic discharge in the gas feed lines to the chamber. RF power may be applied through the substrate support electrode, while the showerhead may be grounded.
Wafer-to-wafer uniformity may be affected by varying reaction temperature from wafer-to-wafer: process conditions, clean cycles, idling time, and change in emissivity of the showerhead components over time can all affect the substrate or wafer as well as the gas reaction temperature. Although after a number of wafers in continuous batch processing the showerheads eventually reach an equilibrium temperature, these factors can affect the equilibrium temperature or the number of deposition cycles before the equilibrium temperature is reached. Also, in a multiple station chamber, showerhead temperature may vary from station to station. For example, the cool incoming wafers at station 1 may lead to a progressive cooling of the showerhead. The thermal cycle of showerheads may also create particles from coatings on the showerhead having different coefficients of thermal expansion from the showerhead itself.
It is therefore desirable to accurately control the temperature of each showerhead in a chamber to create a manufacturing-worthy equipment with best wafer-to-wafer uniformity. The showerhead should be designed without creating particles and be manufacturable at the lowest cost without increasing footprint or reducing throughput while maintaining good wafer-to-wafer uniformity.